1. Field of the Invention
The present invention relates to a group-III nitride (referred to as III-nitride) semiconductor laser device, a method of fabricating the III-nitride semiconductor laser device, and a method of estimating damage from formation of a scribe groove.
2. Related Background Art
Patent Literature 1 describes a laser device. When a principal surface of a substrate is a face tilting at 28.1° from a {0001} plane toward a direction equivalent to the [1-100] direction, secondary cleaved facets are {11-20} planes perpendicular to both of the principal surface and optical cavity faces, and the laser device is of a rectangular parallelepiped shape.
Patent Literature 2 describes a nitride semiconductor device. The back surface of the substrate for cleavage is polished to reduce the total layer thickness to about 100 μm. A dielectric multilayer film is deposited on cleaved facets.
Patent Literature 3 describes a nitride-based compound semiconductor device. The substrate used for the nitride-based compound semiconductor device comprises a nitride-based compound semiconductor with the threading dislocation density of not more than 3×106 cm−2 and the in-plane threading dislocation density is substantially uniform.
Patent Literature 4 describes a nitride-based semiconductor laser device. In the nitride-based semiconductor laser device, cleaved facets are formed as described below. With respect to recesses which are made by etching from a semiconductor laser device layer to an n-type GaN substrate, scribed grooves are formed like a dashed line (at intervals of about 40 μm) in a direction orthogonal to an extending direction of ridge portions, using a laser scriber, while avoiding projections made during the etching of cavity faces on the n-type GaN substrate. Then the wafer is cleaved at positions of the scribed grooves. On this occasion, each of regions without the scribed grooves, e.g., each projection, is cleaved from the adjacent scribed groove as an origin. As a result, each device separation face is formed as a cleaved facet consisting of a (0001) plane of the n-type GaN substrate.
Patent Literature 5 describes a light emitting device. The light emitting device is able to readily emit light at a long wavelength, without deterioration of luminous efficiency in its light emitting layer.
Patent Literature 6 describes a semiconductor laser. In this semiconductor laser, cleavage introduction level-differences for cleavage having the depth of about 20 μm are formed from the top side of a GaN-based semiconductor laser chip in an n-type GaN substrate, a semiconductor layer, and a current block layer. These cleavage introduction level-differences are spaced by the length of the cavity of the semiconductor laser. These cleavage introduction level-differences are formed only in a region opposite to one side of a ridge part. The distance between the cleavage introduction level-differences and the ridge part (optical waveguide) is not less than about 70 μm. The cleavage introduction level-differences are formed in a direction orthogonal to the ridge part 12a (optical waveguide).
Non-patent Literature 1 describes a semiconductor laser in which a waveguide is provided in an off-axis direction and in which mirrors are made by reactive ion etching, on a semipolar (10-1-1) plane.    Patent Literature 1: Japanese Patent Application Laid-open No. 2001-230497    Patent Literature 2: Japanese Patent Application Laid-open No. 2005-353690    Patent Literature 3: Japanese Patent Application Laid-open No. 2007-184353    Patent Literature 4: Japanese Patent Application Laid-open No. 2009-081336    Patent Literature 5: Japanese Patent Application Laid-open No. 2008-235804    Patent Literature 6: Japanese Patent Application Laid-open No. 2008-060555    Non-patent Literature 1: Jpn. J. Appl. Phys. Vol. 46 (2007) L444